1. Field of the Disclosure
This disclosure relates to a backlight unit, and more particularly to a backlight unit adapted to provide an improved external appearance and uniform brightness, as well as a liquid crystal display (LCD) device with the same.
2. Description of the Related Art
Cathode ray tubes (CRTs) correspond to one of display devices which are widely used. The CRTs are mainly used as monitors for TVs, measuring apparatuses, information terminals, and so on. However, the heavy weight and large size of the CRTs have been a major hindrance to the manufacturing of small, light electronic products.
In other words, the CRTs have the limitations of weight and size in the current trend of small, light electronic products. Under such circumstances, LCD devices using an electro-optical effect, plasma display panels (PDPs) using a gas discharge, electro luminescence display (ELD) devices using a electro-luminescent effect, and so on are expected to substitute for the CRTs.
Among the substitutable display devices, LCD devices are being actively researched. Also, LCD devices are gradually being used in a wide range of applications due to their advantages such as lightness, thinness, and low power consumption. Moreover, LCD devices are being manufactured to have even larger screens, be thinner, and consume less power, in order to meet the requirements of users. Such LCD devices display images by controlling the amount of light transmitted through liquid crystal.
The LCD devices are not self-illuminating display devices, unlike CRTs. As such, an LCD device includes a backlight unit provided on the rear surface of an LCD panel. The backlight unit includes a separated light source providing the light necessary to display an image. The backlight unit can be classified as either an edge type or a direct type in accordance with the disposition of a light source.
Such an edge type backlight unit is mainly applied to comparatively small-sized LCD devices such as the monitors of laptops and desk-top computers. The edge type backlight unit has good light uniformity, a lengthened lifespan, and the advantage of making the LCD device thinner.
The direct type backlight unit has begun to be concentrically developed as the LCD device is enlarged to a size above 20 inches. The direct type backlight unit forces light to be directly irradiated onto the entire surface of the LCD panel. To this end, the direct type backlight unit includes a plurality of light sources arranged on the lower surface of a diffusion plate. Since the direct type backlight unit has a higher light efficiency than the edge type backlight unit, it is mainly used for LCD devices of a large size that require a high brightness.
The backlight unit employs a plasma type light source, such as a cold cathode fluorescent lamp (CCFL), a hot cathode fluorescent lamp (HCFL), an external electrode fluorescent lamp (EEFL), an external and internal electrode fluorescent lamp (EIFL), or others, as a light source. Alternatively, the backlight unit uses a light emission diode (LED) as a light source. Particularly, the LED is widely used in the backlight unit because of its features of long lifespan, low power consumption, small size, superior durability, and others.
The LEDs included in the edge type backlight unit are used as a spotted light source. As such, each of the LEDs must have a limited emission angle. Due to this, the edge type backlight unit configured to include the LEDs has a disadvantage causing a brightness difference between regions in which the LED is disposed and not. The brightness difference results from the fact that a lightened portion and a darkened portion are generated on the regions in which the LED is disposed and not, respectively.
Also, the edge type backlight unit must be provided with a critical side space necessary to receive the LEDs. Moreover, the edge type backlight unit must dispose the LEDs to be separate from a light guide plate by a fixed distance. Therefore, it is very difficult to reduce a non-display area corresponding to an edge area of the LCD device without a display area occupying a central portion, below a critical size.